Clauzadea

Clauzadea is a genus of lichen-forming fungi in the family Lecideaceae. The genus contains four species. These lichens grow almost exclusively on limestone and other calcium-rich rocks, often living mostly hidden within the upper layers of the stone with only a faint grey or brown film visible on the surface. They produce small, initially reddish-brown fruiting bodies that darken to black and may sit flush with the rock surface or be sunken so deeply that they leave neat pits when they weather away....read more on Wikipedia.